1. Field of the Invention
The subject matter of this invention concerns a compressed-air screw or bolt tightener according to the precharacterizing part of Patent claim 1, especially an impulse or a torque screw or bolt tightener.
2. Summary of the Invention
Impulse or torque screw or bolt tighteners which are used for a number of different screwing and tightening processes are fitted with a valve with which the bolt or screw tightener is switched on and off. The valve is located along the compressed-air supply line that leads to the screw or bolt tightener. This valve can be actuated manually by the operating personnel or by an electronic measuring and control device. Prior art screw or bolt tighteners, when switched on, operate at a constant pressure throughout the screwing and tightening process. As a result, the same kinetic energy is used to fasten both an M10 screw and an M8 screw. This is undesirable. In certain cases, this constant kinetic energy that is delivered to the screw or bolt tightener may induce the tool to penetrate the material to which the screw or bolt is to be applied and cause a rupture. This may result in damage to the screwed connection. With self-tapping screws, for example, the resistance is higher at the beginning of the screwing process; however, after the sheet metal has been perforated, this resistance drops to nearly zero. Yet, the prior art bolt or screw tightener uses the same high force, and the screw is struck at full force, which may cause the screw or the screw thread to rupture.
The present invention eliminates the problem of the prior-art screw or bolt tighteners mentioned by using a simple structural design which allows adjustment to the actual screwing and tightening needs.